CHAPTER VII

THE MECHANISM OF NATURAL IMMUNITY AGAINST MICRO-ORGANISMS 175 The destruction of micro-organisms in natural immunity is an act of resorption.—Part played by inflammation in natural immunity.—Importance of microphages in immunity against micro-organisms.—Chemiotaxis of leucocytes and ingestion of micro-organisms.—Phagocytes are capable of ingesting living and virulent micro-organisms.—The digestion of micro-organisms in phagocytes is most often effected in a feebly acid medium.—Bactericidal property of serums.—Phagocytic origin of the bactericidal substance.—Theory of the secretion of the bactericidal substance by leucocytes.—Comparison of the bactericidal power of serums and of blood plasmas.—The bactericidal substance of blood serums must not be considered a secretion-product of leucocytes; it remains within the phagocytes, so long as they are intact.—The cytases.—Two kinds of cytases: macrocytase and microcytase.—Cytases are endo-enzymes, allied to trypsins.—Changes in the staining properties and in the form of micro-organisms in the phagocytes.—Absence or rarity of fixatives in the serums of animals endowed with natural immunity.—The agglutination of micro-organisms does not play any important part in the mechanism of natural immunity.—Absence of antitoxic property of the body fluids in natural immunity.—The phagocytes destroy the micro-organisms without their ingestion being preceded by neutralisation of the toxins.